1. Field of the Invention
The present invention relates to a glass funnel for use in a cathode ray tube, especially a television tube. The glass funnel according to the invention relates to a glass funnel including a funnel neck which is cylindrical; a funnel body whose transverse cross-sections change over from a substantially circular shape to a substantially rectangular shape and whose cross-sectional areas grow continuously in a direction moving away from the funnel neck and a parabolic region arranged between the funnel neck and the funnel body and wherein the respective connecting sections of the parabolic region to the funnel neck and the funnel body have corresponding substantially circular cross-sections.
2. Prior Art
This sort of glass funnel is described in WO 98/07174 A2.
Cathode ray tubes are used as an important part of a television set. They include a glass funnel, which forms the evacuated space of the tube together with the television or display screen.
The glass funnel itself has three parts: a neck, which contains the electron beam gun and is cylindrical; a parabolic region, around which a deflection coil for guiding the electron beam is arranged and which has circular transverse cross-sections increasing in area in a direction moving away from the neck and a funnel body whose cross-sectional areas continuously increase and change over from a circular to a substantially rectangular shape, until the cross-sectional area of the television screen is reached. The term xe2x80x9csubstantially or approximately rectangularxe2x80x9d here and in the following means rectangular, but with rounded corners. Also the area of the television screen on which the electron beam acts or strikes is substantially rectangular as well as the television screen itself. This means that a substantial part of the area in the region of the glass funnel having a substantially circular cross-section is unused for passage of the electron beam. Since the deflection coil for guiding the electron beam is arranged outside of the funnel, a greater portion of the energy (about 25%), which is supplied to the coil, must be used for overcoming the distance to the electronic beam by the magnetic field.
EP 0 813 224 A2 describes a glass funnel whose cross-section is substantially circular only in the funnel neck region, but already substantially rectangular at the parabolic region. Because of this feature of their glass funnel the unused portion is reduced and the deflection coil can be mounted closer to the electron beam. This leads to a considerable energy saving. The disadvantage of the approximately rectangular parabolic region suggested in that reference is that there is a significant implosion danger for the cathode ray tube formed with this parabolic region. Very narrow specifications or tolerances are connected with the geometry of the glass funnel or in the type and manner in which the cross-sectional area increases and in the manner in which the parabolic region begins. Sufficient implosion safety is guaranteed only if these specifications are followed closely. From the production engineering point of view there is also the danger that the entire manufacturing process must be rearranged or changed because of the introduction of this entire newly shaped parallel region, since then the glass funnel shape must be greatly changed from its standard form.
It is an object of the present invention to provide a glass funnel of the above-described kind, especially for a cathode ray tube, particularly a television tube, whereby energy is saved in operation of the resulting cathode ray tube formed from the glass funnel and implosions of the cathode ray tube are reliably prevented as much as possible.
This object and others which will be made more apparent hereinafter are attained in a glass funnel including a funnel neck which is cylindrical; a funnel body whose transverse cross-sections change over from a substantially circular shape to a substantially rectangular shape and whose cross-sectional areas grow continuously in a direction moving away from the funnel neck and a parabolic region arranged between the funnel neck and the funnel body and including respective connecting sections to the funnel neck and the funnel body having corresponding substantially circular cross-sections.
According to the invention the parabolic region has at least one part or portion with a substantially rectangular cross-section and the at least one part or portion is located between the respective connecting sections to the funnel neck and the funnel body.
The glass outer surface of the glass funnel on the smaller and larger axes are brought closer to the funnel central axis by means of a substantially rectangular cross-section in a center or middle portion of the parabolic region. The length of this center portion with the substantially rectangular cross-section varies in the centimeter range. Since the electron beam deflection unit sits directly on the glass outer surface, the deflection unit will be brought closer to the electron beam, which extends within the funnel. The magnetic field, which must be built up by the deflection unit to guide the electron beam, must thus pass over a smaller gap or spacing and can be correspondingly much weaker. Because of this aspect of the invention electrical energy is saved.
The larger the spacing to the source of the magnetic field, the greater the spacing of the field lines. Since the magnetic field is now closer to the electron beam, the field line density for the cathode ray tube made with the glass funnel according to the invention relative to the field line density with the standard prior art parabolic region is thus increased and the electron beam can be guided more precisely.
The glass funnel according to the invention may be embodied both in 4:3 format and also 16:9 format, which are the currently recognized screen formats. The energy saving effect of the invention is better, the greater the deflection angle is, which has especially proven to be correct in the cathode ray tubes in the 16:9 screen format. The size of this effect is especially large for deflection angles of 120xc2x0 and larger.
Because the funnel form for the entire glass funnel is changed only in a small portion in the center of the parabolic region relative to a conventional prior art glass funnel, the implosion safety is only made slightly poorer. It has been shown that the stresses developed in the glass increase chiefly in the transition region between the funnel neck and the parabolic region. However this change is only on the order of a percentage, or in the percentage range. No additional features for increasing implosion safety are necessary.
In manufacturing and further processing with the glass funnel according to the invention only regions must be changed which effect the shape of the parabolic region. The additional handling of the glass funnel, as e.g. transport or surface processing, can remain unchanged.
The side ratio of the substantially rectangular cross-section of the parabolic region corresponds to the side ratio of the substantially rectangular cross-section of the funnel body at its opposite end from the funnel neck. On this end the funnel body has the side ratio of the display or television screen. Since the electron beam also covers an area with this same side ratio, the deflection coil can thus be applied or mounted so that it is arranged as close to the electron beam as possible from all sides, when the parabolic region has this same side ratio in the portion with the rectangular cross-section.
In a preferred embodiment of the glass funnel the areas of the successive transverse cross-sections through the parabolic region increases continuously. Preferably the diagonals of the cross-sections increase continuously through the enter parabolic region.